New to the Real Estate Game!! Please read. Any advice is wanted!

[Kevin Thomas]

 Hello there! My name is Kevin, and I am looking to get into Real Estate. I am 21 years old turning 22 next month! I have 2 kids and I am set to be married in a few months. I know this sounds young and financially crazy (2 kids) to start the hike down Real Estate lane... but we are in a perfect spot. I am in a career field of Law Enforcement and she is in her dream field of Orthodontics. We make great money and have 0 student debts.  We just purchased a 2 unit duplex with an attached garage on the bottom. We plan on living downstairs and fixing/renovating the upstairs so it is up to code. Then moving upstairs and repeating with the downstairs unit. Once completed we plan on moving out and renting the whole thing. We have been VERY responsible with our credit scores to this point, so I am the only one on this loan for the duplex. Only 66k. Our goal, in the next year or so, is for her to buy another local property (3 unit single story / apt style) and continue on. We have so many questions as to how to move forward. Is renting the best money gainer when starting from a smaller bank account? Or is foreclosed/short sales and flipping better? Real Estate license a must? Just any kind of TIPS or SUCCESS story's would do wonders for us!!! Thank you in advance for your time. :)